Insulating sheath on electrical conductor strands



1945' J. N. SELVIG 2,379,756

INSULATING SHEATH ON AN ELECTRICAL CQNDUCTOR STRAND Filed Aug. 14, 1941FIG./

INVENTOR J. N. SELVIG- A TTORNEV Patented July 3, 1945 v INSULATINGSHEATH ON ELECTRICAL CONDUCTOR STRANDS John N. Selvig, Westfield, N. Jassignor to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York Application August 14, 1941, Serial No. 406,854

4 Claims.

This invention relates to electrical conductor strands, and moreparticularly to an insulating sheath on an electrical conductor strand.

In some instances electrical conductor wires have of recent years cometo be insulated by forming directly on the wire a continuous seamlesssheath of pulpous insulating material, e. g. paper pulp fibres ofcellulose, felted or intermatted together. Wires thus insulated haveexcellent electrical characteristics for many uses because the sheath offelted fibres contains a high proportion of its volume as air entrappedwithin and between its fibres; and, for many uses, the higher theproportion of air thus held within the gross surface of the sheath, thegreater the useiulness of the sheath as electrical insulation.

An object of the present invention is to provide an insulated conductorhaving an improved sheath of pulpous material as described containing amaterially increased proportion of entrapped air within the grosssurface of the sheath.

With the above and other objects in view, the invention may be embodiedin an electrical conductor wire having an insulating sheath of pulpousmaterial thereon compacted into a substantially grossly continuous andseamless sheath but also formed within the body of the sheath withlongitudinal ducts substantially empty except for air.

Other objects and features of the invention will appear from thefollowing detailed description of one embodiment thereof taken inconnection with the accompanying drawing in which the same referencenumerals are applied to identical parts in the several figures and inwhich Fig. 1 is a broken diagrammatic view in elevation of a pair ofrollers for squeezing a tape of wet paper pulp having a wire embeddedthrein;

Fig. 2 is a plan view of a portion of such tape after squeezing;

Fig. 3 is a section on the line 33 of Fig. 2; and

Fig. 4 is a view similar to Fig. 3 showing the tape formed into acylindrical sheath about the wire.

The general procedure and apparatus for creating a tape of wet pulpousmaterial such as paper pulp, applying a wire to the partially formedtape, completing the tape to contain the wire, and folding and feltingthe tape into a seamless sheath about the wire are old and form no partof the present invention. Hence these are not disclosed here. Suitableprocedure and apparatus for these purposes are disclosed and describedin detail in U. S. Patent 1,615,394 of January 25, 1927,

to J. S. Little, to which reference may be had, if desired, for thesefeatures. Reference is also made to co-pending applications Serial Nos.406,- 852 and 406,853, for apparatus and method for making the sheath,respectively.

In Fig. 1 herein is shown a pair of rolls l0 and H to receive aplurality of fiat ribbons or tapes 20 of wet paper pulp each having ametal wire 2| embedded and contained within it. The lower roll If) isprovided with a surface of hard material, metal, hard rubber, hardfibre, artificial resin or other suitable substance, and is formed withparallel peripheral grooves l2 and i3 of two kinds distributed inrepeated duplications of one set or pattern H for each wire bearing tape20. For clarity, only one tape is shown, but in practise there willusually be a plurality of tapes. The middle groove I3 of each set orpattern ll of grooves is deeper and wider than any other groove of theset and receives and gives passage to that part of the tape 20 whichcontain the wire 2|. On either side of the groove I3 is a plurality ofparallel grooves l2 all preferably alike and equally spaced apart. Theroll II is smooth on its surface and is made to have its outer surfacerelatively soft and elastically yielding, e. g. by making the body ofthe roll throughout of suitable material or by providing a hard coredroll with a surface layer or sheath I5 of suitable material, e. g. softvulcanized rubber, vulcanized corn oil, or the like.

A tape 20 with its wire 2| in passing over the roll I 0, has its lateralportions at each side of the wire 2|, strongly compressed by the roll Hwhere the tape lies on the lands it while the portions between thesecompressed parts are merely pressed down into the grooves |2 by the rollll without any material compression of the substance of the tape inthese portions. Hence the tape emerges from the rolls I0 and Hsubstantially in the state disclosed in Figs. 2 and 3. The longitudinalstrip portions I I8 which were pressed by the lands l8 of the roll IIare thin, dense and tough while the intercalated longitudinal stripportions H2 of the tape which were kept free of pressure by the groovesl2 of the roll III are thick, fluffy and relatively weak.

The longitudinally ridged tape I20 thus created is then wrapped aboutthe wire 2|, as shown in Fig. 4, to form a generally cylindricalseamless sheath 220 about the wire, and the whole is dried. Acharacterizing and important feature of the structure so made, is thepresence in the sheath 220 of longitudinally extending passages 222created by the wrapping of the longitudinally ridged tape I20. It is thepresence of these longitudinal voids, passages or ducts 222 within t edy t e sheath 22! in the finished product that notably increases thevalue of the sheath as an insulator. Another feature of importance isthe presence within the sheath of the longitudinally extending, thin,hard pressed, tough strips 2|! corresponding to the elements H8 in Figs.2 and 3. Paper pulp and fluiiy paper at best have no great tensilestrength, and when the sheathed wire is subjected to more or less severebending or pulling or friction in subsequent manipulation or use theremay be danger of rupture of the sheath, especially transversely of thewire. In the wire shown in Fig. 4 the longitudinal strips 2|! integrallyparts of the sheath have a tensile strength which may be several timesthat of any part of a sheath of undifferentiated structure, and so tendto support and save the sheath 220 as a whole where an ordinary pulpsheath might well be ruptured.

The embodiment of the invention herein disclosed is illustrative and maybe variously moditied and departed from without departing from thespirit and scope of the invention as pointed out in and limited by theappended claims.

What is claimed is:

1. In an insulated electric conductor, a fibrous pulp material, anelectric conductor embedded in the pulp material, said pulp materialhaving a ribbed flap portion to provide air ducts, and said flap portionbeing wrapped around the embedded conductor.

2. In an insulated electric conductor, a-ribbon of pulpous material, anelectric conductive core embedded in the ribbon oi pulpous material, andsaid ribbon having indentations therein to form air ducts when theindented ribbon is wrapped around the embedded core.

3. In an insulated electrical conductor, a sheath of pulpous material,an electrically conductive core embedded in the sheath, the said sheathhaving integrally united strip portions which are dense and toughcontinuously throughout their length and projecting portions which arefluffy and relatively weak continuously throughout their length.

4. In an insulated electrical conductor, a sheath of pulpous material,an electrically conductive core embedded in the material of the sheath,the said sheath having integrally united longitudinal strip portionswhich are dense and tough continously throughout their length, andoutwardly extending portions which are fluiIy and relatively weakcontinuously throughout their length, said strip portions being wrappedaround the embedded conductor to provide longitudinally extending ductswithin the body of the sheath.

JOHN N. SELV'IG.

